Authentication checks are the verification steps used to confirm that a user, service, or device is still being recognized correctly after a system change. They cover logins, API tokens, service accounts, certificates, MFA, and device trust, especially when infrastructure is moved, rebuilt, or reconfigured. In practice, a migration can break or weaken authentication in subtle ways: an account may lose a role, a service token may stop matching, a certificate may no longer be trusted, or a device may fall back to a weaker method.
They matter because authentication failures are both an availability risk and a security risk. If checks are skipped, administrators may not notice that old credentials still work, that a new control is bypassed, or that a service is accepting unauthenticated requests. Attackers often look for these gaps after change events, because rushed cutovers can leave stale accounts, misconfigured identity providers, or overly broad trust between systems. Strong authentication checks help defenders confirm that the new environment validates identities as intended and that only approved users and services can connect.